Carbonate-hosted “Alpine-type” Zn-Pb deposits in the Eastern and Southern Alps – trace element geochemistry and isotopic data of sulphides

Abstract

More than 500 occurrences of carbonate-hosted Pb-Zn ores are documented in the Eastern and Southern Alps. They are invariably hosted by shallow lagoonal and reef carbonates of Middle and more frequently Upper Triassic (Anisian and Carnian) age and are collectively termed “Alpine-type” deposits. The local palaeogeography and synsedimentary structures influenced ore mineralization. Although they occur in a wide region, they share common features such as a simple mineralogical composition, complex ore textures, light sulphur isotopic compositions, Late Palaeozoic Pb model ages, and similar trace element compositions in sphalerite, galena and pyrite. Sphalerite records a low-temperature (60-140°C) precipitation. It is low in Fe, Mn, Co, Ag and In, but commonly contains elevated Cd, Ge, As, Tl and Pb. Galena is Ag-poor, although both sphalerite and galena tend to higher Ag concentrations towards the northern Districts. Minor Fe sulphides are low in Co and Ni but carry considerable As and Tl. Rb-Sr dating of sphalerite from the type locality Bleiberg reveals an age of ≈229 Ma for ores of the Raibl Group, and ages of ≈207 and ≈201 Ma for trace element-rich breccia ore in the western part of the Bleiberg deposit. The older age corresponds to U-Pb ages obtained on calcite associated with the Pb-Zn mineralization at the Gorno deposit (Southalpine). The younger age suggests fluid flow within the carbonate sequence in an extensional tectonic regime due to fracturing of the carbonate platform during initial rifting of the Penninic Ocean.

Calcite U-Pb geochronology of Huayuan carbonate-hosted Zn-Pb mineralization in Central Yangtze Craton, South China

“…The tectonic shifts from compression to transpression or extension are crucial in MVT ore fluid migration and sulfide deposition, corresponding with the geological settings of these deposits 1,3,4,8 . However, the genesis timing of carbonate-hosted deposits is contentious, oscillating between syngenetic, diagenetic, or epigenetic origins 6,9,10 , influenced by prolonged regional compressional tectonics and hydrothermal systems in carbonate-hosted Zn-Pb ore fields 6,9,10 . Despite advances in dating techniques, accurately determining the age of low temperature carbonate-hosted deposits remains complex due to the absence of suitable U-rich minerals, necessitating reliance on alternative dating methods like Rb-Sr and Sm-Nd isochron dating [11][12][13][14][15][16] .…”